This invention relates generally to electronically controlled fuel injection systems and, more particularly, to an apparatus for adjusting the duration of each fuel shot associated with a multi-shot fuel injection to compensate for the inherent delay between electrical activation of the fuel injector and the actual start of fuel injection.
Electronically controlled fuel injectors are well known in the art including mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of the desired timing and quantity of fuel to be injected into the cylinders. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine. Each injection waveform may include a plurality of distinct and/or rate-shaped fuel shots delivered to a cylinder during a particular fuel injection event.
Techniques utilizing multiple fuel injection during an injection event may be utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Multiple fuel injection involves splitting the total fuel delivery to the cylinder during a particular injection event into a number of separate fuel injection shots, such as into two fuel shots generally referred to as a main injection, and an anchor injection.
Due to the construction and operation of mechanically actuated electronically controlled fuel injectors, there is an inherent dead band or delay associated with the commencement of a given injection current pulse and the actual start of fuel injection during the pulse duration. This delay is known in the art as the SOC/SOI delay, that is, the delay from the start of current (SOC) to the start of the injection (SOI).
In prior art mechanically actuated injection systems, the SOC/SOI delay is ignored when calculating the duration of the current pulse necessary to deliver the volume of fuel requested by the governor for the associated fuel shot. Consequently, less than the requested volume of fuel is injected into the cylinder for the given fuel shot. If only one shot is delivered during an injection event, the governor may correct its fuel request to account for the SOC/SOI delay. But when multiple shots are delivered during an injection event, the governor must adjust to additional SOC/SOI offsets for each shot, making it difficult to maintain a steady state engine speed and desired emission level.
It is, therefore, desirable to improve the performance of mechanically actuated electronically controlled fuel injectors by adjusting the duration and/or the rate of fuel delivery for each fuel shot so that the desired volume of fuel for each shot is injected. It is also desirable to adjust the current duration of one or more fuel shot associated with a particular multi-shot fuel injection event in order to compensate for the SOC/SOI delay and to deliver the appropriate and desired amount of fuel during each such fuel shot.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention there is disclosed a fuel injection control system for regulating the injection duration of a fuel shot associated with a multi shot injection event of a fuel injector, the fuel injector having an inherent fuel injection pressure threshold and being in mechanical communication with a cam follower. The system comprises an electronic controller in electrical communication with the fuel injector, the controller being configured to deliver a electronic control signal thereto, and a camshaft having a cam profile in mechanical communication with the cam follower. The cam profile is operable to generate pressure within the fuel injector sufficient to overcome the fuel injection pressure threshold in predetermined intervals in conjunction with the control signal of the electronic controller.